Carbon steel is the most common, cheapest and most versatile metal used in chemical industry for construction of processing and storage equipment. Sulfuric acid is a material which finds wide use in chemical industry. Aqueous sulfuric acid containing less than about 60% by weight of H.sub.2 SO.sub.4 is extremely corrosive with respect to carbon steel, so that carbon steel is not a suitable material of construction for processing and storage equipment for sulfuric acid at these concentrations. At concentrations of more than about 60% by weight of H.sub.2 SO.sub.4 and up to about 100% H.sub.2 SO.sub.4, carbon steel will generally show corrosive attack of less than about 0.02" per year at temperatures below 100.degree. F. At temperatures above about 100.degree. F., carbon steel is not a suitable material of constructions for sulfuric acid service involving sulfuric acid of concentration between about 60% and about 93% by weight. For sulfuric acid of that concentration, at temperatures above about 100.degree. F., suitable materials of construction include glass, silicon iron, Hastelloy B and D (T.M.) Durimet 20 (T.M.), Worthite (T.M.), lead, Monel (T.M.), impervious graphite, tantalum, gold, platinum, zirconium, and molybdenum. However, even at temperatures below about 100.degree. F. aqueous sulfuric acid containing between about 60% and 100% H.sub.2 SO.sub.4, especially between about 78% and about 93% by weight H.sub.2 SO.sub.4 is sufficiently corrosive towards carbon steel to cause severe concern from a safety standpoint, and to make use of carbon steel equipment uneconomical because of the high frequency with which the equipment must be repaired or replaced because of corrosive failure.
The present invention provides a cheap yet effective corrosion inhibitor to reduce corrosive attack of sulfuric acid containing more than about 60% by weight of H.sub.2 SO.sub.4 on carbon steel, at temperatures below as well as above about 100.degree. F. and up to about 150.degree. F.